1. Field of the Invention
This invention relates to illumination systems, and more particularly, to an edge-lit illumination system having separate light extracting and light directing components.
2. Description of the Prior Art
Both light extraction and direction in an illumination system using a single light directing array (LDA) are typically accomplished by the same LDA that is intimately coupled, i.e. physically and optically, to a waveguide. The dual functionality of the LDA (i.e. light extraction and direction) requires that the LDA be fabricated separately from the waveguide and then secured thereto by lamination, adhesive, etc. The LDA typically comprises a plurality of three-dimensional prisms (e.g. pyramidal) that contact only a portion of the light output surface of the waveguide and provide a contact area between the LDA and the waveguide of less than 100%, e.g. typically between 8% and 20%. The overall rigidity of the waveguide and the tendency of the separately fabricated LDA to warp over time causes the LDA to separate from the waveguide, resulting in failure of the illumination system. Furthermore, optical coupling between the LDA and waveguide is subject to stringent requirements, and even minor disturbances affect the performance of the illumination system.
There exists a need in the art for an illumination system having light extraction and direction features that overcome the above-described shortcomings of the prior art.